The overall aim of this project is to improve and expand in animal models of human cancer the method of cancer radioimmunodetection. Radioimmunodetection involves the administration of radioactive antibodies to tumor-specific or tumor-associated substances and the use of total-body scintigraphy to visualize areas of abnormal radioactivity presumably reflecting sites of tumor. Previous studies performed by us have shown the feasibility of this method of tumor detection and localization with radioactive antibodies to carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), and human chorionic gonadotropin (HCG), making use of a computer-assisted subtraction method for tumor image enhancement. Using xenografted human cancers containing the appropriate antigenic markers, the project will have four major objectives: (1)\prepare and evaluate, in comparison to whole IgG, the use of antibody fragments (Fab, Fab', and F[ab']2) against CEA, HCG, AFP, and a new colorectal cancer marker, colon-specific antigen-p (CSAp); (2)\develop and evaluatethe possible advantage of using monoclonal antibodies to these tumor markers for improved tumor mixtures, such as to CEA + CSAp and to HCG + AFP in tumor models having the binary marker combinations; and (3)\attempt to improve tumor image enhancement techniques by use of normal IgG labeled with a different isotope of the same atom as used to label the specific antibody preparation (e.g., 131-I-antibody/123-Inormal IgG or 111-In-antibody/113m-In-normal IgG). (2)